Conventional advertising depends on keywords. Advertisers specify bid amounts on keywords for their campaigns. As a result, queries that express a concept relevant to the advertiser, but using long tail words that the bidder did not specify, do not hit the ad. Furthermore, queries that use the bid keywords in an expression of a topic unrelated to the advertisers market will hit the ad irrelevantly.
Another problem with the conventional approach is that ad buyers may only specify a fixed bid amount per keyword, regardless of the relevance of concepts and particular semantic information related to user expressions. Though ad providers have performed much research and development into ways for ad buyers to maximize relevance to content and optimize the efficiency of money spent, ad buyers are at the mercy of ad providers' keyword and bid amount algorithms.